A black hole devours everything, even light. Yet it obeys the laws of physics: it possesses entropy — a measure of the hidden information an object 'remembers.' In the 1970s, Jacob Bekenstein and Stephen Hawking discovered a strange pattern: a black hole's entropy grows not with its volume, but with the area of its event horizon — the imaginary surface from which nothing returns. It's like a book whose text is written not on the pages, but only on the cover.
The new work reveals where this area comes from. The horizon can be divided into minuscule cells the size of the Planck length (the smallest meaningful scale, about 10⁻³⁵ meter). These cells are like identical mosaic tiles. Physicists counted how many ways they can be rearranged without changing the overall picture. This counting yields two contributions. The first depends on the number of tiles and accounts for the area. The second, a logarithmic correction, is fixed and independent of the black hole's size.
The approach is valuable for its generality and minimal assumptions. It hints that spacetime really is made of discrete 'atoms,' and a black hole is the perfect proving ground to study them. Someday this will help build a theory of quantum gravity, and thus understand the workings of the Universe at the deepest level.
Contrary to the image of an all-devouring abyss, a black hole turns out to be a thrifty archivist: its surface stores everything that ever fell in. And the mosaic on the horizon continues to surprise.
If a black hole's hidden information depended on volume, a black hole with Earth's mass could store more information than all the books ever written by humanity. But nature chose area, and that's the key to the holographic principle, which suggests our three-dimensional Universe might be a projection from a two-dimensional surface.
In Stanisław Lem's novel 'Fiasco,' black holes are described as 'information graveyards,' but modern physics sees them not as graveyards, but as libraries at the boundary of spacetime.